Interpretive Summary: Sweet onion (Allium cepa L.) is not a very competitive crop due to its slow growth rate, short height, non-branching plant structure, low leaf area, and shallow root system; therefore, weed competition can devastate onion production. The weed control challenges for onion production are even greater for those considering organic crop production. Research was conducted at Lane, OK, to determine the impact of acetic acid applications on broadleaf weed control in onions, 'Candy' and 'Cimarron.' The experiment included 6 weed control treatments (2 application volumes, 2 hand weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications. Nutsedge and grass weeds were selectively removed to investigate the impact of the acetic acid on the broadleaf weeds. Vinegar (20% acetic acid) was applied as an over-the-top broadcast application at 50 or 100 gpa on April 21, 2007 using four 8002 nozzles on 20 inch spacing. Within each application volume (50 and 100 gpa) plots were either handweeded or the uncontrolled weeds were allowed to grow. Weed control ratings were collected throughout the growing season. Weed control peaked at 7 DAT, averaging 95% and 99% total broadleaf weed control for the 50 and 100 gpa application volumes.

Technical Abstract:
Weed control is a major challenge in conventional and organic production systems, especially for organically produced sweet onion (Allium cepa L.). Although corn gluten meal shows great promise as an organic preemergent herbicide for onions, research has shown the need for supplemental, postemergent, weed control once the early season effectiveness of corn gluten meal diminishes. Acetic acid is an approved organic postemergent herbicide that may have potential to affectively provide post-emergent weed control. Research was conducted at Lane, OK, to determine the impact of acetic acid applications on broadleaf weed control in onions, 'Candy' and 'Cimarron.' The experiment included 6 weed control treatments (2 application volumes, 2 hand weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications. Nutsedge and grass weeds were selectively removed to investigate the impact of the acetic acid on the broadleaf weeds. Vinegar (20% acetic acid) was applied as an over-the-top broadcast application at 50 or 100 gpa on April 21, 2007 using four 8002 nozzles on 20 inch spacing. Within each application volume (50 and 100 gpa) plots were either handweeded or the uncontrolled weeds were allowed to grow. Weed control ratings were collected throughout the growing season. Weed control peaked at 7 DAT, averaging 95% and 99% total broadleaf weed control for the 50 and 100 gpa application volumes.